This invention relates generally to the fabrication of thin films of vaporizable solids on substrates.
More specifically, this invention relates to the fabrication of thin films by impacting particles of controlled size, grown from a vapor, upon a substrate surface.
Traditional methods for the manufacture of thin films having semiconducting properties involved slicing large single-crystal ingots grown by the Czochralski process. As the ingots are generally a few square inches in cross sectional area and of round shape, this factor alone severely restricts the usefulness of such films for solar cell arrays and other large area devices. In addition, ingot growth, slicing and subsequent processing steps are high cost batch processes which are not adaptable to large scale continuous production techniques.
It is also known that many of the elements can be vapor deposited directly on substrates and that decomposable compounds may be utilized to deposit elements upon a substrate heated to a temperature above the decomposition temperature of the compounds. In the case of vapor deposition of an element upon a substrate, there is ordinarily required the maintenance of a high vacuum within the reactor. Although decomposable compounds do not necessarily require high vacuum conditions for their deposition, this technique is limited by the small selection of compounds having properties adaptable for this purpose.
Silicon in sheet form is also fabricated by pulling molten silicon into a ribbon through a narrow slit in a crucible. A generally similar technique involves formation of a ribbon by pulling a web of silicon out of a container of molten silicon. Both of these processes require contact of molten silicon with non-silicon solids with attendant problems of contamination.